Evaluation of a Heat Exchanger Designed for Efficient Fine Particle Precipitation in Small-Scale Wood Combustion

There is a need to develop feasible PM reduction methods for small-scale biomass combustion installations due to their high PM emissions. In this work, we evaluated the potential of a novel prototype small-scale heat exchanger (PHX) designed for high particle emission reduction. In addition, the role of the different deposition mechanisms in such an application was studied. The PHX was connected to a wood-fired unit, and both particle and gas emissions and thermal efficiencies were evaluated. In addition, a scrubbing system, for keeping the PHX walls clean, was connected to the system. The thermal efficiency reached over 100% due to the recovered heat by water condensation, when operating the PHX at temperatures typical for floor heating. The usage of the scrubber for cleaning the PHX increased the PM1 emissions, compared to the heat exchanger (HX) reference case, but prevented fouling of the PHX tubes. The PHX was found to have fine particle precipitation efficiencies of 45% and 48%, depending on applied water temperatures. The particle reduction was mainly a result of thermophoretic deposition in the heat exchanger tubes.